The invention is especially suited for use in a process and apparatus for producing particles of stockpileable asphaltic concrete from hot-mix asphaltic concrete and will be described in that connection.
Heretofore, one of two methods of repairing defective road beds have been employed. In one method a cutback asphaltic concrete is used. Cutback asphaltic concrete is a mixture of sand and stones, usually referred to as aggregates, with cutback asphalt cement as a binder. Cutback asphalt cement is one which has been rendered liquid at normal atmospheric temperatures by mixing it with cutback agents such as naphtha or kerosene. Such cutback agents are necessary to maintain workability of the material and to allow it to remain loose in a stockpile. This is what is meant by the term "stockpileable" as it is used in this specification and in the appended claims. A stockpileable material is one which remains loose and workable and does not fuse into a large, hard, agglomerate mass, at normal atmospheric temperatures.
With respect to cutback asphaltic concrete, the presence of cutback agents, required to make the concrete workable at normal atmospheric temperatures, also serves to weaken the material. Thus, cutback asphaltic concrete is easily displaced by traffic and its use permits only temporary repair of road beds.
The second method of repairing road beds utilizes hot-mix asphaltic concrete. Hot-mix asphaltic concrete also consists of a combination of aggregates coated with asphalt cement, however, no cutback agents are used; heat is employed to maintain workability. Both the aggregate and the asphalt cement are heated prior to mixing to dry the aggregate and obtain sufficient fluidity of the asphalt cement for proper mixing and workability: hence the term "hot-mix". Thus, hot-mix asphaltic concrete is only workable when hot. If it cools it becomes hard and unworkable; this results in much waste.
The term "asphaltic concrete" as used in this specification and in the appended claims does not include cutback asphaltic concrete (i.e., any asphaltic concrete utilizing a cutback agent to maintain workability at normal atmospheric temperatures). The manual on "Design and Construction of Asphaltic Roads and Streets" published by The Asphalt Institute in 1952 defines asphaltic cement as "a refined asphalt which must be heated for use and must be used with hot sand and rock". This clearly excludes cutback asphaltic cements as they do not depend on heat for workability.
The stockpileable asphaltic concrete of this invention remains workable at normal atmospheric temperatures without cutting agents by virtue of the unique process of manufacture disclosed by this specification. It is used, as needed, in whatever quantity required. To make a permanent repair the material is spread to the desired level and heat is applied by torch, hot iron or preferably by infra-red waves. The application of heat causes the stockpileable asphaltic concrete of this invention to revert to its original state as hot-mix asphaltic concrete. There is no substantial waste as unheated portions of the particulate material can be returned to the stockpile for later use. The stockpileable asphaltic concrete of this invention will not rejoin into an unworkable mass so long as the stockpile temperature does not exceed 120.degree. F.
It is an object of this invention, therefore, to provide a new and improved stockpileable asphaltic concrete which obviates the above-mentioned disadvantages of prior art materials.
It is another object of this invention to provide a new process for making stockpileable asphaltic concrete.
It is a further object of this invention to provide apparatus for producing stockpileable asphaltic concrete.